1. Field of the Invention
The present invention relates to a pager or similar radio selective calling receiver and more particularly to a receipt frequency search control method for a radio selective calling receiver.
2. Description of the Related Art
It has been customary with a radio selective calling receiver to receive a signal having a single particular frequency and, if the signal includes an ID (identification) number assigned to the receiver, alerts the user of the receiver to the receipt of a message while displaying the message. The problem with this kind of conventional receiver is that the receiver cannot receive a service in areas different in frequency from a single area assigned to the receiver.
A multiarea service allowing a radio selective calling receiver to receive a service over a plurality of areas is an implementation recently proposed to solve the above problem. A radio selective calling receiver authorized to receive a multiarea service is required to search for one of a plurality of frequencies allocated to the current area, and then receive a signal having the frequency searched for. For this purpose, the receiver sequentially searches the frequencies registered thereat and thereby detects a signal which it can received in the current area.
However, the conventional receiver to receive the multiarea service has some problems left unsolved, as follows. A period of time necessary for the receiver to search all of the registered frequencies once increases in proportion to the number of registered frequencies. It follows that as the number of registered frequencies increases, the time when the receiver detects a synchronizing signal is delayed in areas servicing at frequencies to be searched at a late stage of search, delaying the time of synchronization. The receiver is therefore apt to miss a call meant for the pager. In addition, power consumption is aggravated with an increase in search time.
In light of the above, Japanese patent laid-open publication No. 7-122975 proposes a radio selective calling receiver capable of promoting efficient search and reducing a search time. Specifically, the receiver taught in this document registers frequencies not needing search at a skip memory as skip frequencies, and does not search the skip frequencies at the time of search. This kind of scheme, however, requires the user of the receiver to register the skip frequencies at the skip memory beforehand by troublesome operation.
Further, Japanese patent laid-open publication No. 6-244777 discloses a radio selective calling receiver constructed to sense field strengths during the first search cycle and then rearrange a searching order for the second search cycle on the basis of the sensed field strengths, thereby promoting efficient frequency searching. However, this procedure is effective only for the second and successive search cycles following the first search cycle failed to determine a receipt frequency. Further, conditions may differ from the first search cycle to the second and successive search cycles. In addition, the first search cycle and the second and successive search cycles must always be effected in combination, limiting efficiency available with the receiver.
It is therefore an object of the present invention to provide a radio selective calling receiver capable of efficiently searching a plurality of frequencies without resorting to any extra operation, e.g., registration of frequencies, and a frequency search control method therefor.
In accordance with the present invention, a radio selective calling receiver includes a memory storing a plurality of frequencies each corresponding to a particular area in which a service is available. A receipt frequency control section sequentially searches the frequencies stored in the memory to thereby determine a frequency capable of being received in the current area. A timepiece counts time. A synchronized frequency storage stores, for each of the frequencies, the number of times of synchronization set up at each preselected sampling time together with the sampling time. When frequency search begins, the receipt frequency control section sequentially searches the frequencies in order of the number of times of synchronization set up at a sampling time closest to a frequency search start time at which the frequency search has begun, the frequency having the greatest number of times being first.
In a preferred embodiment, the receipt frequency control section determines, when frequency search begins, a first and a second sampling time closest and second closest to a frequency search start time when the frequency search has begun, weights the numbers of times of synchronization respectively set up at the first and second sampling times by weights inversely proportional to a difference between the search start time and the first sampling time and a difference between the search start time and the second sampling time, respectively, produces a sum of the weighted numbers of times, and sequentially searches the frequencies in order of the size of the sum, the frequency having the greatest sum being first.
In another preferred embodiment, the receipt frequency control section determines, when frequency search begins, a first and a second sampling time closest and second closest to a frequency search start time when the frequency search has begun, produces a sum of the numbers of times of synchronization respectively set up at the first and second sampling times, and sequentially searches the frequencies in order of the size of the sum, the frequency having the greatest sum being first.